Assessment of the Style and Timing of Surficial Deformation Along the Central Reelfoot Scarp, Lake County, Tennessee

Abstract

Stratigraphic and structural relations exposed in a 90-m-long trench across the Reelfoot scarp in the central New Madrid Seismic Zone (NMSZ) provide data to assess the style and timing of late Holocene tectonic surficial deformation in the central NMSZ. Near-surface deposits exposed in the trench include natural levee, overbank, colluvial, and liquefaction-related deposits. The levee deposits consist of fine-grained, cross-bedded sands and silty sands and are overlain by clayey overbank and scarp-derived colluvial deposits. Liquefaction-related features include sand dikes and sills that intrude into the levee and overbank deposits, and a possible older extrusive sand deposit. Charcoal and archaeological artifacts from a deposit inset into and overlying the levee deposits suggest that the levee deposits are older than about A.D. 800 to 900. Charcoal from the overbank deposits yielded an age estimate of cal. A.D. 1310 ± 90; charcoal from the overlying colluvial deposits yielded an age estimate of cal. A.D. 1540 ± 90. Distinct marker beds within the levee deposits define a broad monocline that parallels the ground surface and exhibits more than 5 m of down-to-the-east vertical separation. This fold consists, in part, of four smaller-scale flexures each having amplitudes of about 1 m. Associated with these flexures are numerous west-dipping normal faults that have a total net vertical separation of about 0.4 m in a down-to-the-west sense, which is opposite in sense to that exhibited by the scarp and the silty marker beds. We interpret that these faults are related to extension in the crest of the monocline, and that the monocline represents deformation above a west-dipping reverse fault that reaches or approaches the ground surface east of the trench and the base of the scarp. At the trench site, this interpretation places the surface projection of the fault near the western margin of Reelfoot Lake. Stratigraphic relations exposed in the trench and several shallow boreholes permit identification of at least one and possibly three late Holocene earthquakes. Stratigraphic relations and age-estimates best support the interpretation that the unweathered liquefaction related features exposed in the trench are a result of the 1811–12 earthquakes, and that the scarp-derived colluvial deposits are a result of a prior event. Radiocarbon analyses show that this penultimate event occurred between about A.D. 1310 and A.D. 1540. Stratigraphic evidence of a third event prior to about A.D. 900 is present but equivocal. Given that the most-recent event occurred in A.D. 1812, we estimate that the time between the two most-recent earthquakes large enough to produce liquefaction and/or surface deformation was about 200 to 600 years.

Northern Extension of the Tennessee Reelfoot Scarp Into Kentucky and Missouri

“…Fuller's (1912) classic paper was the most comprehensive early study to present evidence of co-seismic deformation associated with these earthquakes. Subsequent studies have supported Fuller's tectonic origins of northwestern Tennessee landforms that include the Reelfoot Lake basin, the Lake County uplift, and the most obvious tectonic landform, the Reelfoot scarp (Stearns, 1979;Hamilton and Zoback, 1982; Champey Pocket Site~ (Donaldson ~e) Russ, 1982;Crone and Brockman, 1982;Stahle et al, 1992;Kelson et al, 1992;in press;Van Arsdale el al., 1994). The Reelfoot scarp is the topographic boundary between the Reelfoot Lake basin and the Tiptonville dome ( Figure 1, inset B).…”

“…Reelfoot Lake is believed to have formed by the damming of the predecessor west-flowing Reel Foot River during 1811-1812 uplift of the Tiptonville dome (Van Arsdale et al, 1991;Stahle et al, 1992). The Reelfoot scarp is the surface expression of a west-dipping reverse fault that lies within the left-stepping restraining bend in the New Madrid seismic zone (Russ, 1982;Crone and Brockman;1982;Sexton and Jones, 1986;Chiu et al, 1992;Kelson et al, 1992;in press;Schweig and Ellis, 1994). Russ (1982) described the scarp as an east-facing monocline with minor extensional normal faulting based on his trench across the scarp (Figure 1).…”

“…More recent trench excavations and a seismic reflection survey have revealed a reverse fault at the base of the scarp at the Proctor City site (Figure 1), thus suggesting that the Reelfoot scarp is the eastern limb of a fault propagation fold in press;Van Arsdale et al, 1994). Several trenches ( Figure 1) excavated across the scarp revealed that the scarp's surface topography parallels folded near-surface sediments (Russ et al, 1978;Kelson et al, 1992; in press). Trench excavations (Kelson et al, 1992; in press) and coring data presented below reveal that locally the fold amplitude is greater than the scarp amplitude because of post-folding deposition on the down-thrown (eastern) side of the scarp.…”

“…Several trenches ( Figure 1) excavated across the scarp revealed that the scarp's surface topography parallels folded near-surface sediments (Russ et al, 1978;Kelson et al, 1992; in press). Trench excavations (Kelson et al, 1992; in press) and coring data presented below reveal that locally the fold amplitude is greater than the scarp amplitude because of post-folding deposition on the down-thrown (eastern) side of the scarp. In general, however, the topography of the Reelfoot scarp closely mirrors the tectonic folding associated with the underlying Reelfoot fault .…”

Spatial and Temporal Characteristics of Paleoseismic Features in the Southern Terminus of the New Madrid Seismic Zone in Eastern Arkansas

“…Dating, measuring, and interpretation of many large liquefaction features over a broad region have led to the development of a New Madrid event chronology (Tuttle, 1999;. Kelson et al (1992Kelson et al ( , 1996, Schweig (1995), Li et al (1998), have documented liquefaction features from at least two seismic events occurring prior to the 1811-1812 earthquakes. These two events occurred A.D. 900 _+ 100 years and A.D. 1450 _+ 150 years and were likely similar in strength to those of 1811 and 1812 .…”